Have you tried on other client machines and with different browsers? Stupid question probably, but do all the files end with .pdf? (we have had some weird problems with files uploaded from Mac OS9 which does not bother with file suffixes)

Also, check your web server error logs - just in case something is going wrong in the download and the file is getting truncated - you might see something there.

on my moodle site for some reason pdf docuemtns will not load - strange but if you change the file name so that it has no spaces in it- this will work! but i am not willing to do that for every pdf document that get uploaded.

We have added a self-signed SSL Certificate to our site and everything seems to be working well except for serving up Certificates to students in the inline frame (instructors get them as file download link).

We are on 1.9. Does anyone have any updated header changes to make and in what files? When I browse around I am not seeing anything that looks relevant in any "file.php". The closest I could find was a few sections in ./moodle/lib/filelib.php.

I have not had any luck with the force download option from the activity settings for the certificate via course edit mode. I am also retesting that to make sure I just was not seeing the change due to some sort of cache / proxy.

are you using IE? See here for a possible tip: if it will work (what is your IE version?), it could be possibile to arrange lib/filelib.php::send_file() to address such issue without requiring any fix client side.

Thank you Matteo.. I will take a look at that function and see if I can get the right recipe of header options in place to get it working.

We are using Apache on RedHat on the server side. Our students are primarily using IE 8 (Unless they also login at home / their own laptops they are not local admins.. IE 8 is probably the majority situation since they have time allotted to work on the PCs they are provided). There would be little that we could do to feasibly influence much more for changes on how the client side is managed beyond us being an allowed / trusted site. So we definitely need our fix to be something something mainly on our side.

you can also try to add $CFG->disablebyteserving = true to your config.php to avoid Adobe plug-in to take just pieces of your PDF in order to decrease the time required to view the PDF especially for large files (any workaround could have some drawbacks...).

Note: last Microsoft KB for IE 8 is 323308 and Moodle code seems to be complaint to those notes.